Establishing seasonal and alert influenza thresholds in Cambodia using the WHO method: implications for effective utilization of influenza surveillance in the tropics and subtropics

Self Cite

Background Influenza virus circulation is monitored through the Cambodian influenza‐like illness (ILI) sentinel surveillance system and isolates are characterized by the National Influenza Centre (NIC). Seasonal influenza circulation has previously been characterized by year‐round activity and a peak during the rainy season (June‐November). Objectives We documented the circulation of seasonal influenza in Cambodia for 2012‐2015 and investigated genetic, antigenic, and antiviral resistance characteristics of influenza isolates. Patients/Methods Respiratory samples were collected from patients presenting with influenza‐like illness (ILI) at 11 hospitals throughout Cambodia. First‐line screening was conducted by the National Institute of Public Health and the Armed Forces Research Institute of Medical Sciences. Confirmation of testing and genetic, antigenic and antiviral resistance characterization was conducted by Institute Pasteur in Cambodia, the NIC. Additional virus characterization was conducted by the WHO Collaborating Centre for Reference and Research on Influenza (Melbourne, Australia). Results Between 2012 and 2015, 1,238 influenza‐positive samples were submitted to the NIC. Influenza A(H3N2) (55.3%) was the dominant subtype, followed by influenza B (30.9%; predominantly B/Yamagata‐lineage) and A(H1N1)pdm09 (13.9%). Circulation of influenza viruses began earlier in 2014 and 2015 than previously described, coincident with the emergence of A(H3N2) clades 3C.2a and 3C.3a, respectively. There was high diversity in the antigenicity of A(H3N2) viruses, and to a smaller extent influenza B viruses, during this period, with some mismatches with the northern and southern hemisphere vaccine formulations. All isolates tested were susceptible to the influenza antiviral drugs oseltamivir and zanamivir. Conclusions Seasonal and year‐round co‐circulation of multiple influenza types/subtypes were detected in Cambodia during 2012‐2015.

Section: Discussionsupporting

confidence: 91%

Section: Discussionmentioning

confidence: 99%

Circulation and characterization of seasonal influenza viruses in Cambodia, 2012‐2015

Horwood

Karlsson

Horm

et al. 2019

Self Cite

“…β( t ) is the transmission coefficient, representing the probability of transmission per contact between an infected and a susceptible individual. As influenza transmission intensity changed during an epidemic season and the duration of each intensity varied, we assumed different values of β corresponding to three different infectious times in this study. σ is the rate at which an exposed individual becomes infectious per unit of time.…”

Section: Methodsmentioning

confidence: 99%

Influenza illness averted by influenza vaccination among school year children in Beijing, 2013‐2016

Zhang

Cao

Costantino

et al. 2018

BackgroundThe benefit of school‐based influenza vaccination policy has not been fully addressed in Beijing.ObjectivesTo evaluate the benefit of school‐based influenza vaccination policy launched in Beijing.MethodsUsing existing surveillance and immunization data, we developed a dynamic transmission model to assess the impact of influenza vaccination in school‐going children. The outcome was defined as the averted number of medically attended influenza illnesses and the prevented disease fraction to all children aged 5‐14 years for the 2013/14, 2014/15, and 2015/16 seasons.ResultsWe estimated that during the three consecutive influenza seasons, the averted number of medically attended influenza illnesses among children aged 5‐14 years was around 104 000 (95% CI: 101 000‐106 000), 23 000 (95% CI: 22 000‐23 000), and 21 000 (95% CI: 21 000‐22 000), respectively. Corresponding prevented fractions to all children aged 5‐14 years were 76.3%, 38.5%, and 43.9%.ConclusionsIn Beijing, school‐based vaccinations reduced a substantial number of medically attended influenza illnesses despite seasonal variation in the prevented fraction. This is strong supportive evidence for the continuation of school‐based vaccination programs to reduce the influenza burden in this age group.

“…Cambodia has conducted influenza surveillance since 2009, including both outpatient influenza‐like illness surveillance and hospitalized SARI surveillance, and enrolls all patients meeting the Cambodia SARI case definition at eight sentinel surveillance sites. Surveillance has demonstrated that influenza viruses commonly circulate during the rainy season (June‐November) in Cambodia each year 13, 14. Between 2009 and 2014, influenza circulation peaked between August and November; influenza positivity among SARI cases fluctuated from 12% in 2009 to 3% in 2014 15…”

Section: Introductionmentioning

confidence: 99%

“…Surveillance has demonstrated that influenza viruses commonly circulate during the rainy season (June-November) in Cambodia each year. 13,14 Between 2009 and 2014, influenza circulation peaked between August and November; influenza positivity among SARI cases fluctuated from 12% in 2009 to 3% in 2014. 15 To better understand the impact of influenza on the Cambodia population and inform possible future vaccine policy, health officials are exploring best practices to estimate the burden of influenzaassociated SARI in the country.…”

Section: Introductionmentioning

confidence: 99%

Using a hospital admission survey to estimate the burden of influenza‐associated severe acute respiratory infection in one province of Cambodia—methods used and lessons learned

Stewart

Sar

et al. 2018

Self Cite

BackgroundUnderstanding the burden of influenza‐associated severe acute respiratory infection (SARI) is important for setting national influenza surveillance and vaccine priorities. Estimating influenza‐associated SARI rates requires hospital‐based surveillance data and a population‐based denominator, which can be challenging to determine.ObjectivesWe present an application of the World Health Organization's recently developed manual (WHO Manual) including hospital admission survey (HAS) methods for estimating the burden of influenza‐associated SARI, with lessons learned to help others calculate similar estimates.MethodsUsing an existing SARI surveillance platform in Cambodia, we counted influenza‐associated SARI cases during 2015 at one sentinel surveillance site in Svay Rieng Province. We applied WHO Manual‐derived methods to count respiratory hospitalizations at all hospitals within the catchment area, where 95% of the sentinel site case‐patients resided. We used HAS methods to adjust the district‐level population denominator for the sentinel site and calculated the incidence rate of influenza‐associated SARI by dividing the number of influenza‐positive SARI infections by the adjusted population denominator and multiplying by 100 000. We extrapolated the rate to the provincial population to derive a case count for 2015. We evaluated data sources, detailed steps of implementation, and identified lessons learned.ResultsWe estimated an adjusted influenza‐associated 2015 SARI rate of 13.5/100 000 persons for the catchment area of Svay Rieng Hospital and 77 influenza‐associated SARI cases in Svay Rieng Province after extrapolation.ConclusionsMethods detailed in the WHO Manual and operationalized successfully in Cambodia can be used in other settings to estimate rates of influenza‐associated SARI.